For IC cards used as cache cards, credit cards, tickets of transportation systems (such as trains and buses), etc., identification functions of identifying the users of IC cards are important, and security enhancement is being increasingly important with the expanding use of IC cards. In recent years, some memory cards, which have been used only to save personal data, are also provided with the identification functions, and advancement in the identification functions of portable devices has become a technical challenge.
Under such circumstances, researches and developments on using variation in the characteristics of individual devices as “chip fingerprints” are in progress. These are known as physically unclonable function (PUF). For example, there is known a technology of using distribution of crystal defects in a predetermined area of a semiconductor substrate as an ID for identifying the semiconductor substrate itself.
With the technology of the related art using factory-default distribution of crystal defects as an ID, the distribution of crystal defects is assumed to remain unchanged. As is well known, however, a semiconductor chip suffers from much deterioration over time while being used, and the distribution of crystal defects of the semiconductor chip thus changes from the factory-default state in many cases. There are therefore problems in the related art that identification becomes difficult and the accuracy of authentication is lowered as the period of use (the number of uses) of a device increases and the defects increase.